A New Free-Floating Planet Candidate

by Paul Gilster on November 14, 2012

Planets without stars may exist throughout the galaxy, and some studies suggest that there may be more so-called ‘rogue planets’ than main sequence stars. Now we get word of an object called CFBDSIR2149, associated with the stream of young stars called the AB Doradus Moving Group, a group of about 30 stars of the same age and metallicity associated with the star AB Doradus. The object turned up at infrared wavelengths in the Canada-France Brown Dwarfs Survey (CFBDS), which is looking for cool brown dwarf stars. If the object is indeed part of the AB Doradus group, then we can deduce that it is young (50-120 million years) and, according to this ESO news release, a number of its other properties can be inferred.

Image (click to enlarge): This image captured by the SOFI instrument on ESO’s New Technology Telescope at the La Silla Observatory shows the free-floating planet CFBDSIR J214947.2-040308.9 in infrared light. This object, which appears as a faint blue dot at the centre of the picture and is marked with a cross, is the closest such object to the Solar System. It does not orbit a star and hence does not shine by reflected light; the faint glow it emits can only be detected in infrared light. The object appears blueish in this near-infrared view because much of the light at longer infrared wavelengths is absorbed by methane and other molecules in the planet’s atmosphere. In visible light the object is so cool that it would only shine dimly with a deep red colour when seen close-up. Credit: ESO/P. Delorme

If the association with the AB Doradus group is assumed, then the possible planet is thought to be 4-7 times the mass of Jupiter, with an effective temperature of 430 degrees Celsius. This is the first time an isolated planet has been identified as part of a moving group, but the possibility remains that the association with the group is purely a matter of chance, in which case we could be looking at a small brown dwarf. However, if it really is a rogue planet, CFBDSIR2149 would be a useful find, according to Philippe Delorme (CNRS/Université Joseph Fourier, France):

“These objects are important, as they can either help us understand more about how planets may be ejected from planetary systems, or how very light objects can arise from the star formation process. If this little object is a planet that has been ejected from its native system, it conjures up the striking image of orphaned worlds, drifting in the emptiness of space.”

Bear in mind that we have had previous candidates for this kind of planet, including ‘free floating’ planets in the Orion Nebula (Philip Lucas and Patrick Roche, 2009), planetary mass objects near the star σ Orionis (Maria Rosa Zapatero Osorio, et al., 2000) and a population of ‘unbound or distant Jupiter-mass objects’ discovered through gravitational microlensing (MOA/OGLE, 2011). At about 100 light years from Earth, this new object would be the closest yet to our Solar System, an intriguing candidate for future study and the first to which we could assign an age.

The new work, led by Delorme, interestingly speculates that a small number of low-gravity late T-dwarfs may turn out to be free-floating planets.’ From the paper:

The conclusions for stellar and planetary formation models would also be far reaching. Either the planetary mass-ﬁeld brown dwarfs are mostly the result of a stellar formation process, which would conﬁrm the fragmentation of a molecular cloud can routinely form objects as light as a few Jupiter masses, [or] these objects are mostly ejected planets. In this case, given that massive planets are less easily ejected from their original stellar system than lower mass ones, and that lighter planets are much more common than heavier ones (see Bonﬁls et al. 2011, for instance), this would mean free-ﬂoating, frozen-down versions of Jupiters, Neptunes and perhaps Earths are common throughout the Milky Way interstellar ranges.

See Island Hopping to the Stars for more on this as seen through the work of Louis Strigari (Stanford University), who speculates that there may be up to 105 compact objects per main sequence star in the galaxy that are greater than the mass of Pluto.

The paper is Delorme et al., “CFBDSIR2149-0403: a 4-7 Jupiter-mass free-floating planet in the young moving group AB Doradus?” Astronomy & Astrophysics 14 November 2012 (preprint).

so .. How do we find the oes closer still to earth? this one is very warm and young.. any close to us are likely to be far older ( closer tot he age of our solar system, which is average for this part of the galaxy) and colder. We already have a pretty good list of warm – ish brown dwarfs, though cool brow dwarfs or ones in the general direction of the milky way ( crowded sky) may have eluded WISE eyes. We need a new survey scope that is in the meter + class operating at high data rates and large Field of view… from space. WFIRST or the new European scope is the next step but we need more, something on the order of 3 meters with a gigapixel infrared camera and one minute plus exposure times to cover the sky every month.
a mission ot a rogue planet nearby woudl really make a difference. 1,000 AU plus distance….

I see no particular reason to come down one side or the other on the question of whether this object is a planet or a low mass brown dwarf (non-fusing star). The authors of the paper even note in their introduction that stellar formation processes do appear to be able to produce objects below the deuterium-fusion threshold.

Calling these objects planets is more likely to lead to headlines I guess…

I remember Strigari’s hypothesis from when it was posted here. However, since that time, the WISE telescope has found fewer than the expected number of brown dwarfs. Extrapolating down in size from brown dwarfs down to Pluto size objects suggest that interstellar space may be less filled with these objects than Strigari thinks.

Also, could existing radar astronomy equipment detect any of these objects that were within, say, 1/10th (or even 1/100th) of a light year from the Sun? If not radar, could a space-based microwave radiometer (similar in principle to the one Mariner 2 carried to measure the temperature of Venus’ surface) detect any nearby free-floating planets by their feeble radio emissions?

jkittle, I was a bit surprised when I read the paragraph in the paper about the WISE detection. From what it sounds like, in WISE, this object is a marginal detection. Yet a ground-based instrument has detected it and measured its properties.

I wonder if the WISE capabilities, for detecting objects like this, were “over sold”, and in reality there are still large possibilities for nearby objects to exist.

I do not doubt that many (most?) rogue planets have been ejected from solar systems as a result of n-body interactions. But I wonder whether ejection from a stellar system is their only possible origin. Interstellar matter can coalesce into ‘objects’ as small as 2-atom molecules. Is coalescence into planet-size objects impossible?

djlactin, there are several papers where planetary mass objects are observed to be formed along with stars, in star-forming clouds. That is, the implication is that they form via the same mechanism as stars. These are large jovians upwards that we are talking of. But I think that is the lower limit in mass for this mechanism. Earth-mass objects seem to be thought of only as forming as planets.

kzb
WISE wa hampered by its short mission time. even one more year would have mad a big difference in the ability to detect motion in neighborhood objects. the Scope was still working on the most important data channels when it was turned off to save a few million dollars ( out of a total development cost of 400 million) politically, Nasa wanted to clear the way for WFIRST ( which subsequently died when the JWST ate up all the funding) WISE is still out there and could be turned on to get new data after 2 years of motion by potential targets. Right now we have no way to follow up on the huge number of marginal detections that were not obviously strong brown draft candidates

Giving the IIE somewhere to go rather than a fixed point in empty space may be the impetus for getting this mission funded. I can see the difficulty in trying to explain to those who usually hold the purse strings why they should spend money on a probe that will not seem to go anywhere. This rogue world, planet or brown dwarf (or Worldship?), may make all the difference, even if it is still tough to reach at this point.

The Pioneers and Voyagers have shown just how much there is to learn way beyond Pluto and these probes were not even meant to be interplanetary explorers. Add a real goal/target like CFBDSIR2149 and you may have a winning combination.

I am also willing to bet that this is hardly the only rogue world out there, or the closest to the Sol system.

djlactin, here is a new paper on the stellar formation mass distribution, extended down to the planetary mass region (but lower limit still several Jupiter masses). There are other papers with the same conclusion, and that is the formation frequency of such bodies is lower than that of stars. But it’s still substantial.

“Spectroscopy of brown dwarf candidates in IC 348 and the determination of its substellar IMF down to planetary masses”

Astronomers find planets in strange places and wonder if they might support life. One such place would be in orbit around a white or brown dwarf. While neither is a star like the sun, both glow and so could be orbited by planets with the right ingredients for life.

No terrestrial, or Earth-like planets have yet been confirmed orbiting white or brown dwarfs, but there is no reason to assume they don’t exist. However, new research by Rory Barnes of the University of Washington and Renï¿œ Heller of Germany’s Leibniz Institute for Astrophysics Potsdam hints that planets orbiting white or brown dwarfs will prove poor candidates for life.

Book Review: Cry from a Silent Planet, a science fiction novel by John Rowland

Scientists around the globe are fascinated by and continuously hunt for life outside of Earth, as well as in extreme conditions on Earth. Projects such as SETI, the Search for Extraterrestrial Intelligence, scan the skies hunting for alien signals. The Kepler spacecraft increasingly adds to our tally of known extrasolar planets, buoying our prospects for habitable ones, and here on Earth, scientists like Dr. Robert Ballard have helped discover extremophile organisms living on hydrothermal vents deep within Earth’s oceans, once thought inhospitable to life. Life, it turns out, is possible under somewhat varying conditions. Does it exist elsewhere in our solar system or beyond? Astrobiologists believe the answer is “yes.”

Then, recently, the astronomy world was given a present in the form of a confirmed rogue exoplanet. Rogue planets are believed to exist, but only recently were researchers able to observe this particular drifting planet, homeless because it is not orbiting a star.

With additional review, scientists might determine this world is moving through space with a group of young stars, the AB Doradus Moving Group. The planet is located approximately 100 light years from us.

Enter the world of science fiction. The plausible line between science and science fiction meet on a plane mixing reality and conjecture. In the new novel Cry from a Silent Planet, author John Rowland walks the tight rope of that line.

An alien civilization lives underground because their dying star has scorched the surface of their home planet. Making matters worse, an incoming rogue black star appears to be on a gravitational collision course with them. This is the recipe for the riveting start of Cry from a Silent Planet.

Charter

In Centauri Dreams, Paul Gilster looks at peer-reviewed research on deep space exploration, with an eye toward interstellar possibilities. For the last nine years, this site has coordinated its efforts with the Tau Zero Foundation, and now serves as the Foundation's news forum. In the logo above, the leftmost star is Alpha Centauri, a triple system closer than any other star, and a primary target for early interstellar probes. To its right is Beta Centauri (not a part of the Alpha Centauri system), with Beta, Gamma, Delta and Epsilon Crucis, stars in the Southern Cross, visible at the far right (image: Marco Lorenzi).

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